1. Field of the Invention
The present invention relates to a remote maintenance system for a digital communication network consisting of a plurality of digital switching offices.
2. Description of the Related Art
A digital communication network comprises a plurality of local switching offices (LOs) and a toll center (TC). Recently, the maintenance of equipment at each LO has remotely executed at a centralized maintenance and operation center (CMOC) located at the TC. The maintenance system of thus using the CMOC will be called a remote maintenance system hereinafter. The CMOC has two functions: a maintenance function and an operation function. The operation function is for the administration of the network, such as setting or changing subscribers only the maintenance function at the CMOC will be discussed in this disclosure.
As one of the remote maintenance systems of the prior art, a first remote maintenance system of the prior art will be discussed referring to FIGS. 1 and 2. In FIGS. 1 and 2, the supervisory information at each LO 1 is sent to the CMOC 3 through an exclusive data line (DL) 41 provided independently from a digital transmission line (DTL) 51 for ordinary communication in the digital communication network. As shown in FIG. 2, in the prior art, the operating status data and alarm data at the LO are gathered at an alarm unit (ALM) 10. Then, these data are sent to a data sending unit (SND) 16 through a bus line 100 in the LO 1 and are sent to the CMOC 3 through the DL 41.
The data for the operating status and alarm sent from the LO 1 are received at a data receiving unit (RCV) 36 in the CMOC 3. Then, in the CMOC 3, the data received at the RCV 36 are processed by a main processor (MPR) 31, displayed on a visual display unit (VDU) 351 of a system control work station (SCWS) 35, and stored in a memory means such as a magnetic tape (MT) 34. When a fault occurs in the LO 1, the existence of the fault is signalled by an alarm indicator or buzzer, which are not depicted in FIG. 2, to an operator at the CMOC 3. Then, the operator at the CMOC 3 investigates the fault by observing the visual display unit (VDU) 351 of the SCWS 35. The operator then informs an operator stationed at the LO1 how to repair the fault by, for example, telephone, using the digital communication network.
When the operator at the LO 1 receives the maintenance information for repairing the fault from the operator at the CMOC 3, the operator at the LO 1 repairs the fault at the LO 1 in accordance with the maintenance information from the operator at the CMOC 3. The operator at the LO 1 executes the maintenance to the system in accordance with the maintenance information by observing a VDU 151 and operating an operating console 152 of a SCWS 15 at the LO 1.
Thus, in the first remote maintenance system of the prior art, the data of the operating status and alarm at the LOs 1 are remotely supervised at the CMOC 3. However, the operator at the CMOC 3 must call the operator at the LO 1 to inform the LO operator how to repair the fault and an LO operator must always be stationed at each LO 1 for executing the maintenance. Further, a memory such as a magnetic tape (MT) 14 also must be provided at the LO 1 for, e.g. initial programming in response to a serious fault, such as a system-down in the LO 1. The system-down is a system problem wherein the switching operation ceases due to a hardware problem of the switching network or a software problem in the main processor. These hardware problems most occur because of a problem of the software for the main processor. Previously considering the occurrence of such system-down, the MT 14 is provided for storing an initial loading program used for normally restarting the switching network and/or main processor. Reference symbols DTs 13 and 33 in FIG. 2 indicate digital terminals of the DL 51 provided between the LO 1 and the CMOC 3.
To improve the above problem of the first remote maintenance system of the prior art, there is a second remote maintenance system of the prior art as shown in FIGS. 3 and 4. In FIGS. 3 and 4, the same numerals and symbols as in FIGS. 1 and 2 designate the same units or functions as in FIGS. 1 and 2. In the second remote maintenance system of the prior art, maintenance data from the CMOC 3 are also sent to respective LOs 1 through an exclusive data line. In FIG. 3, a one dot chain line having reference numeral 42 indicates a data line through which the data are transmitted in both ways between each LO 1 and the CMOC 3. As shown in FIG. 4, the maintenance data from the CMOC 3 is transferred to the LO 1 through a second DL 422. That is, when a fault occurs in the LO 1, the operator at the CMOC 3 provides the maintenance data for the LO 1 by operating an operating console 352 while observing a VDU 351 of a SCWS 35. The maintenance data entered made by the operator at the CMOC 3 is sent from a data sending unit (SND) 37 in the CMOC 3 to an RCV 17 in the LO 1 through the DL 422.
The second remote maintenance system of the prior art has the following merits compared with the first remote maintenance system of the prior art: (1) there is no need to use the telephone to send the maintenance data from the CMOC 3 to the LO 1; second, (2) there is no need to have the operator always standing by at the LO 1; and (3) there is no need to provide the MT 14 at the LO 1 because the initial loading to overcome the system-down can be executed by the maintenance data sent from the CMOC 3 through the DL 422. In the above, merits (2) and (3) particularly contribute to reducing the maintenance costs for the network. However, the second remote maintenance system has a drawback in that two exclusive data lines (DLs) 41 and 422 are necessary, which causes an increase in the facility costs and the running costs.
As far as reducing the cost for the exclusive data line, there is a third remote maintenance system of the prior art, which uses the DTL 51 for transferring the operating status and alarm data from the LO 1 to the CMOC 3. This system has been disclosed in U.S. Pat. No. 4,575,839 to Yusuke Ogata et al. entitled "CENTRALIZED SUPERVISORY SYSTEM" which issued Mar. 11, 1986. FIGS. 5 and 6 illustrate the system of Ogata as the third remote maintenance system of the prior art. According to the third system of the prior art of Ogata, the operating status and alarm data from the LO 1 to the CMOC 3 are transferred through some channels of the DTL 51. The DTL 51 transfers the data under a pulse code modulation (PCM) system. One dot chain lines 43 in FIGS. 5 and 6 indicate the channels. In FIG. 6, the operating status and the alarm information in LO 1 are gathered at the ALM 10, and the data of the information are created at the ALM 10 and sent to a common channel signaling equipment (CSE) 18 through a bus line 100. Then, the data are sent, under an ordinary common channel signaling system, to a local digital switching 12 network (NW). through an interface unit (INT) 19. Wherein, the ordinary common channel signaling system is, as is well known, the very peculiar system used in the recent digital switching system. Thus, the operating status and alarm data are sent to the CMOC 3 through the NW 12 and the DT 13 in the LO 1 and the DTL 51 by using the channels 43. In the CMOC 3, the operating status and alarm data are sent to the MPR 31 through an NW 32, an INT 39 and a CSE 38, and processed in the MPR 31 so that the operating status and alarm data are stored in the MT 34 and displayed on a VDU in the SCWS 35. The INT 39 is an interface between the NW 32 and the CSE 38, and the CSE 38 is for sending data and signals under the common channel signaling system.
In the Ogata system, the exclusive data line becomes unnecessary to transmit the operating status and alarm data from the LO to the CMOC. However, the maintenance data from CMOC 3 to the LO 1 cannot be transmitted through the DTL 51. Accordingly, an operator must be stationed at the LO 1 and the MT 14 also must be provided at the LO 1, which is functionally similar to the case of the first remote maintenance system of the prior art.